Fetal Ultrasound

Test Overview

Fetal ultrasound is a test done during pregnancy that uses
reflected sound waves to produce a picture of a
fetus, the organ that nourishes the fetus (placenta), and the liquid that surrounds the fetus
(amniotic fluid). The picture is displayed on a TV
screen and may be in black and white or in color. The pictures are also called
a sonogram, echogram, or scan, and they may be saved as part of your baby's
record.

Fetal ultrasound is the safest way to check for problems
and get information about your fetus, such as its size and position. It does
not use
X-rays or other types of radiation that may harm your
fetus. It can be done as early as the 5th week of pregnancy. The sex of your
fetus can sometimes be determined by about the 18th week of pregnancy.

A combination of screening tests using ultrasound may be
done in the first
trimester to look for
birth defects, such as Down syndrome. The
first-trimester screening test uses an ultrasound measurement of the
thickness of the skin at the back of the baby's neck (nuchal translucency) and
the blood levels of free beta-HCG and a protein called pregnancy-associated
plasma protein A (PAPP-A) to check for problems.

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Look at the size and position of the fetus, placenta, and
amniotic fluid.

Determine the position of the fetus,
umbilical cord, and the placenta during a procedure,
such as an
amniocentesis or umbilical cord blood
sampling.

Detect major birth defects, such as a neural tube defect
or heart problems.

3rd-trimester fetal
ultrasound is done to:

Make sure that a fetus is alive and
moving.

Look at the size and position of the fetus, placenta, and
amniotic fluid.

Transvaginal ultrasound is generally done early in a
pregnancy to determine fetal age or to detect a suspected
ectopic pregnancy. It is occasionally done late in
pregnancy to determine the location of the placenta or in a high-risk pregnancy
to monitor the length of the
cervix.

How To Prepare

You may need a full
bladder for the test. If so, you will be
asked to drink water or other liquids just before the test and to avoid
urinating before or during the test. Usually women in the third trimester do not need to have a full bladder.

For a
transvaginal fetal ultrasound, the vaginal transducer is usually covered with a
latex sleeve and a vaginal lubricant, such as K-Y Jelly. If you are allergic to
latex, tell the health professional before having the test.

Talk
to your doctor about any concerns you have regarding the need for the fetal
ultrasound, its risks, how it will be done, or what the results will mean. To
help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).

How It Is Done

Most often, a fetal ultrasound is
performed by an ultrasound technologist. But it may be done by a
radiologist or
obstetrician. Fetal ultrasound can be done in a
doctor's office, hospital, or clinic.

Often you do not need to remove
your clothes for the ultrasound test. You can lift your shirt and push down the
waistband of your skirt or pants. If you are wearing a dress, you will be given
a cloth or paper covering to use during the test.

Transabdominal ultrasound

You may need to have a full
bladder. A full bladder helps transmit sound waves and
pushes the intestines out of the way of the uterus. This makes the ultrasound
picture clearer.

You will not be able to urinate until the
test is over. But tell the ultrasound technologist if your bladder is so full
that you are in pain.

If an ultrasound is done during the later part of
pregnancy, a full bladder may not be needed. The growing fetus will push the
intestines out of the way.

You will lie on your back on a padded
examination table. If you become short of breath or lightheaded while lying on
your back, your upper body may be raised or you may be turned on your side.

A gel will be spread on your belly.

A small, handheld
instrument called a transducer will be pressed against the gel on your skin and
moved across your belly several times. You may watch the monitor to see the
picture of the fetus during the test.

When the test is finished, the gel is cleaned off of your
skin. You can urinate as soon as the test is done. Transabdominal ultrasound
takes about 30 to 60 minutes.

Ultrasound technologists are trained
to gather images of your fetus but cannot tell you whether it looks normal or
not. Your doctor will share this information with you after the
ultrasound images have been reviewed by a radiologist or
perinatologist.

Transvaginal ultrasound

You do not need to have a full
bladder.

You will lie on your back with your hips slightly
raised.

A cover (such as a condom) will be placed over the thin
vaginal transducer. The transducer will be inserted gently into your vagina,
and then it will be moved and rotated to adjust the view displayed on the
monitor. Some doctors may allow you to insert the transducer into your vagina
yourself.

Transvaginal ultrasound takes about 15 to 30
minutes.

How It Feels

During a transabdominal ultrasound, you
may have a feeling of pressure in your bladder. The gel may feel cool when it
is first applied to your belly. You will feel a light pressure from the
transducer as it passes over your belly.

There is normally no
discomfort involved with a transvaginal ultrasound. You may feel a light
pressure when the transducer is moved in your vagina.

Risks

There are no known risks linked with a fetal
ultrasound, either to the mother or fetus. But you may feel anxious if the
ultrasound reveals a problem with your pregnancy or fetus.

"Keepsake video operations" are ultrasound centers that sell ultrasound videos
as your baby's first photo. The U.S. Food and Drug Administration (FDA)
recommends ultrasound scans only to obtain medical information about the fetus.
Keepsake video operations may use the ultrasound machine at higher energy
levels and for longer times than needed to get a "good picture."

What To Think About

Your doctor may recommend
more tests or procedures if the results of your fetal ultrasound are not
normal.

A photograph or videotape of the ultrasound
image of the fetus is sometimes available to you.

Your due
date may be changed based on an ultrasound done in early pregnancy if the
ultrasound predicts a different date, based on fetal size and
development.

Ultrasounds do not always show birth
defects.

In the third
trimester, fetal ultrasound does not accurately
determine fetal age or weight.

The effects of prolonged fetal
ultrasound exposure have not been determined. So the U.S. Food and Drug
Administration (FDA) does not recommend fetal ultrasound for nonmedical
reasons, such as for identifying the sex of the fetus or as personal keepsakes.

Three-dimensional (3-D) fetal ultrasound is being
tested for use in evaluating fetal abnormalities. It is not yet widely
available.

Doppler ultrasound (or duplex scanning) uses reflected
sound waves to estimate the speed and direction of blood as it flows to the
placenta and within the fetus. For more information, see the topic
Doppler Ultrasound.

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